Updated from 7:07 a.m.

NEW YORK (TheStreet) -- Here are 10 things you should know for Tuesday, June 30:

1. -- U.S. stock futures were rising in the face of a potential Greek debt default. It's likely to be a rocky day in the market as investors wrestle with uncertainty over Greece's -- and Europe's -- future.

European markets fell again on Tuesday with literally hours to go until Greece defaults on a €1.5 billion ($1.7 billion) debt payment to the International Monetary Fund, due at midnight. London's FTSE 100, Frankfurt's DAX and Paris's CAC 40 all fell moderately.

Asian stocks were back in positive territory Tuesday after a bad few days. Hong Kong's Hang Seng rose more than 1%, and Japan's Nikkei rose as well.

2. -- The economic calendar in the U.S. on Tuesday includes the comparable store sales Redbook at 8:55 a.m., the S&P Case-Shiller home price index at 9 a.m., the Chicago Purchasing Manager Index at 9:45 a.m., and consumer confidence numbers at 10 a.m.

St. Louis Federal Reserve Bank President James Bullard and New York Federal Reserve Bank President William Dudley will both give speeches on Tuesday.

3. -- U.S. stocks on Monday fell sharply as fears over Greece's debt load reached a fever pitch. The S&P 500 has now given up almost all of its 2015 gains.

The Dow Jones Industrial Average (DIA) - Get Report plummeted 1.95% to 17,596.35. The S&P 500 (SPY) - Get Report flopped 2.09% to 2,057.64. The Nasdaq (QQQ) - Get Report slid 2.4% to 4,958.47.

4. -- The big question is whether Greece will pay the €1.5 billion ($1.7 billion) debt payment it owes to the IMF today. Emergency talks are ongoing to try to salvage the payment, but Greece has indicated that it does not plan to pay the bill. The debt negotiations will dominate the news today and will continue to have a serious effect on global markets.

If Greece doesn't pay on time, it will violate the terms of its bailout deal. That could result in a wider loss of debt financing in Greece as well as a forced exit from the euro currency.

Greece holds a national referendum on July 5. Prime Minister Alexis Tsipras is describing it as a vote on austerity, but it looks like a proxy vote for or against staying in the euro.

If Greece leaves the euro -- a "Grexit" -- the damage to the currency union and to the European project could be substantial and long-lasting. Spain's Prime Minister Mariano Rajoy has warned that a Greek departure from the currency could eventually push other countries out in times of economic difficulty.

5. -- Although the government of Puerto Rico owes $72 billion, its governor, Alejandro Garcia Padilla, said that the commonwealth could not pay the debt. In a speech Monday, Padilla called for a renegotiation of debt terms and said the only alternative to that was a default. Yet Puerto Rican debt is generally ineligible for bankruptcy.

The Puerto Rican debt load also affects investors in municipal bond funds, several of which hold the island's higher-yielding bonds.

6. -- Cenovus Energy (CVE) - Get Reportwill sell its oil and gas royalty business to the Ontario Teachers' Pension Plan. The deal, for Canadian $3.3 billion (U.S. $2.7 billion), is expected to be finalized in July.

Cenovus' U.S.-listed ADR was down 5.22% on Monday and was rising by 3.4% in premarket trading.

7. -- Food distributor Sysco (SYY) - Get Reportis giving up on its planned merger withUS Foods after a judge ruled against the merger. The $3.5 billion deal had been in the works for a year and a half. Sysco will now need to regroup and formulate a new plan for how to expand. The combined company would have held about 25% of the U.S. food distribution market.

In premarket trading, Sysco stock was down 0.8%.

8. -- The turmoil in markets Monday drove investors to safer assets. The CBOE Volatility Index I:VIXjumped 34%, the biggest jump in a session in 2015. Yields on the benchmark 10-Year Treasury fell to 2.3%.

Meanwhile, gold prices rose 0.52% to $1,179.30 an ounce.

9. -- Celgene (CELG) - Get Report will spend $1 billion over 10 years to partner with Juno Therapeutics (JUNO) to create treatments for immune system-based diseases, the companies announced. The biotech companies hope that new products will be available for 2020.

In premarket trading, Juno stock is up 31.9% on the announcement, while Celgene stock was rising by 0.07%.

10. -- ConAgra Foods (CAG) - Get Report reports earnings before the opening bell.